Add minimum documentation on how to generate a font bitmap.

Author: aentinger

README.adoc

@@ -28,3 +28,10 @@ Lesser General Public License for more details.
 You should have received a copy of the GNU Lesser General Public
 License along with this library; if not, write to the Free Software
 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+
+== How-to generate bitmaps from the fonts ==
+[source,bash]
+----
+cd extra
+./generate_font.py 5x7.bdf Font_5x7.c Font_5x7
+----